How a heat pump moves heat uphill

A heat pump does not make heat. It carries heat from a colder place to a warmer one by squeezing a refrigerant until it is hotter than the room, letting it shed that heat, then dropping its pressure so it turns cold enough to soak up heat from outdoors again.

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Heating Cooling

Outdoor air

Indoor air is held at 70°F.

Step through it

CompressorSqueezes low pressure vapor into hot, high pressure vapor. This is where the electricity goes.
Condenser coilThe hot vapor gives its heat to the air and condenses into a warm liquid.
Expansion valveA narrow restriction drops the pressure, and the liquid flashes partly to vapor and gets very cold.
Evaporator coilThe cold refrigerant absorbs heat from the air passing over it and boils back into vapor.
Reversing valveSwaps which coil is indoors and which is outdoors, so the same machine heats in winter and cools in summer.

Why it can beat a space heater

An electric resistance heater turns one unit of electricity into one unit of heat. A heat pump spends its electricity running a compressor and moves heat that already exists outdoors, so it can deliver several units of heat for each unit of electricity. That ratio is the coefficient of performance, or COP.

The readout above shows the theoretical ceiling for COP, set only by the two temperatures the refrigerant works between. Real equipment reaches a fraction of that ceiling because of friction, fan power and heat exchanger losses, so treat the number as a way to see the trend, not as a rating.

The trend to notice: as the outdoor air gets colder in heating mode, the temperature lift grows and the ceiling falls. That is why cold climate heat pumps lean on better compressors and refrigerants, and why some systems keep backup heat.

The same loop, in every fridge and air conditioner

A refrigerator and a window air conditioner run the identical four step cycle. They simply have no reversing valve, so heat only ever flows one way: out of the box or out of the room.

Where Avid uses this

Avid's founder started as an HVAC apprentice at 16. The same thermodynamics shows up in our agricultural work, from cold storage for specialty crops to greenhouse climate control.

Sources

How Does a Heat Pump Work?ENERGY STAR
Heat Pump SystemsU.S. Department of Energy

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